Superabsorbing fibers and films and processes for preparing same

ABSTRACT

Superabsorbent fiber and film compositions comprising partially acidified, hydrolyzed, internally plasticized, crosslinked, superabsorbing fibers or film derived from polysuccinimide and processes for preparing same.

BACKGROUND OF THE INVENTION

[0001] This invention relates to superabsorbing polymers based onL-aspartic acid in synthetic fiber and film forms and to process(es) forpreparing such fibers and films.

[0002] Polysuccinimide (PSI) is prepared by thermal polycondensation ofL-aspartic acid which can then be base-hydrolyzed to polyaspartate saltwhich has many industrial uses such as lubricant in metalworking fluids.Crosslinking PSI before or after hydrolysis renders the hydrolyzed saltsuperabsorbent in that it can absorb many times its weight of liquidsuch as water. This capability of absorbing significant quantities offluids, including body exudates and aqueous compositions of all kinds,creates another important class of application for these polymers inproducts such as diapers, sanitary napkins, incontinence products,towels, tissues and the like. These superabsorbing polymers are in theprior art as typically disclosed in U.S. Pat. No. 5,461,085 (Nagatomo etal); U.S. Pat. No. 5,525,703 (Kalota) and U.S. Pat. No. 5,612,384 (Rosset al). Though articles of superabsorbing polymers derived fromL-aspartic acid are recognized in this art as desirable, to date theyare only disclosed in unshaped, particulate form as recovered from thehydrolysis step forming the salt. Note all the examples of the patentsreferenced above. Continued absence in the art of these polymers infiber or film form is likely due to the important conflictingrequirements of being sufficiently plastically extensible to permitdrawing fiber or forming film while being crosslinked and hydrolyzed tocreate superabsorbency.

[0003] In view of the noted applications, it would be highly desirableto provide biodegradable superabsorbent polymers derived from L-asparticacid in fiber or film form to facilitate formation into products such asdiapers and the like.

[0004] The superabsorbent fibers and films of the present inventionprovide a solution to many problems encountered with unshaped,particulate superabsorbent polymers derived from L-aspartic acid. Forexample, the superabsorbent fibers of the invention have the advantagesof (1) avoiding the problem of migration by having the ability toentangle with fluff pulp fibers, (2) being compatible with other fibersresulting in greater flexibility in applications and fabrication, and(3) having a large surface area resulting in a faster absorption rate.For example, the superabsorbent films of the invention have theadvantage of avoiding the problem of migration by having the ability toremain stationary within an article containing the film.

SUMMARY OF THE INVENTION

[0005] Now, significant developments have been made in producingsuperabsorbent polymer fibers and films derived from L-aspartic acid.

[0006] Accordingly, a principal object of this invention is to producesynthetic, superabsorbent fibers and films of L-aspartic acidderivatives.

[0007] Another object is to provide a method for producing such fibersor films.

[0008] A further object is to chemically modify PSI to render it capableof drawing into fiber or forming film.

[0009] Yet another object is to provide an intermediate precursor forproduction of fibers or films based on PSI prepared from L-asparticacid.

[0010] Other objects will in part be obvious and will in part appearfrom the following detailed description.

[0011] These and other objects are accomplished by the followingmultiple aspects of the invention.

[0012] i) A fiber- or film-forming plastic composition must besufficiently plastically extensible to permit forming into film ordrawing into a filament-like shape without fracture. It is difficult todraw fibers or form films from crosslinked and hydrolyzed PSI which hasnot been further modified. This problem is remedied by one aspect of theinvention by forming an uncrosslinked, non-hydrolyzed, internallyplasticized poly(imide-co-amide) intermediate precursor which is usefulin later forming such superabsorbing polymeric fibers or films. Theintermediate is prepared by reacting a regulated amount of about 1 toabout 20% of succinimide groups of the PSI with a minor, internallyplasticizing amount of one or more monoamine compounds, such asdiethanolamine. The partial amidation with the monoamine compoundsoftens the polymer and facilitates subsequent drawing into fiber formor forming into film. For example, the poly(imide-co-amide) intermediateproduced using diethanolamine as the monoamine compound has repeatingstructural units represented by formula (1)

[0013] and repeating structural units represented by formula (2)

[0014] the mole fraction of repeating structural units represented bythe formula (1) being about 0.01 to about 0.20.

[0015] ii) The internally plasticized poly(imide-co-amide) intermediateis subsequently hydrolyzed to convert essentially all of the succinimidegroups into aspartate groups. A portion of the aspartate groups in thepolyamide produced as a result of the hydrolysis are then partiallyacidified to produce a partially acidified, hydrolyzed, internallyplasticized polysuccinimide composition.

[0016] iii) Since fiber- or film-forming polymer cannot be effectivelydrawn or formed when crosslinked, another aspect of the inventionincorporates crosslinking agent into the partially acidified,hydrolyzed, internally plasticized polysuccinimide composition beforeshaping fiber or film from the crosslinkable but uncrosslinkedintermediate composition. Crosslinking aspartate groups of the polymeroccurs after fiber or film formation in an after-treating or curing stepby subjecting the fibers or film to crosslinking conditions to renderthem capable of superabsorbing. Premature crosslinking is minimized oravoided by incorporating heat reactive crosslinking agents into thecomposition at low temperature, i.e. from or about 0° C. to or about 25°C.

[0017] iv) Products of the process differ from those previously known inthat the superabsorbing polymer is importantly in fiber or film form.The crosslinked fibers or film are of polyamide containing at leastthree divalent or polyvalent moieties randomly distributed along thepolymer chain having the following formulas:

[0018] where A represents hydrogen, alkali metal cation, ammonium,quaternary ammonium or mixtures thereof, R represents a divalent orpolyvalent crosslinker moiety, x, y and z represent mole fractions ofthe moieties in the polyamide and are respectively about 0.01 to 0.20;about 0.40 to 0.90 and about 0.01 to 0.50 wherein the sum of x, y and zis 1.0, and n is an integer from 0 to 4. R₁ and R₂ are substituents onthe monoamine compound used for the internal plasticization of PSI andcan be the same or different. Optionally, the superabsorbent polymercontains minor amounts of unreacted succinimide repeating units, i.e.repeating unit disclosed in formula (2) above, and unreacted acidifiedaspartate repeating units, i.e. repeating unit disclosed in formula (4)herein. As used herein, a minor amount of succinimide repeating units oracidified aspartate repeating units is an amount up to that amount whichhas a detrimental effect on the absorbency properties of thesuperabsorbent fiber or film.

[0019] v) In a specific aspect of the invention, a process is providedfor preparing superabsorbing fibers or film which comprises thefollowing steps in the recited sequence:

[0020] i) condensation polymerizing L-aspartic acid to formpolysuccinimide (PSI) having a weight average molecular weight of atleast about 20,000 Daltons;

[0021] ii) reacting about 1 to about 20% of the succinimide groups ofthe PSI with one or more monoamine compounds to form an internallyplasticized poly(imide-co-amide) intermediate;

[0022] iii) hydrolyzing essentially all of the succinimide groups of thepoly(imide-co-amide) to form an internally plasticized polyamide;

[0023] iv) acidifying about 1 to 50% of the aspartate groups of thepolyamide of iii);

[0024] v) admixing crosslinker with the partially acidified polyamide ofiv) under non-crosslinking conditions to form a crosslinkable,uncrosslinked, partially acidified, hydrolyzed, internally plasticizedPSI composition;

[0025] vi) drawing fibers or forming film from the composition of v);and

[0026] vii) subjecting the fibers or film to crosslinking conditions tocrosslink uncrosslinked aspartate groups and form the superabsorbingfibers or film.

DETAILED DESCRIPTION OF THE INVENTION

[0027] Synthetic superabsorbing polymer fibers and films of theinvention are derived from L-aspartic acid starting monomer availablecommercially from Solutia Inc. L-aspartic acid is conventionallycondensation polymerized in the presence of catalyst such as phosphoricacid. Processes for preparing homopolymer polysuccinimide (PSI) aredescribed in U.S. Pat. Nos. 5,057,597; 5,315,010 and 5,319,145.Molecular weight (weight average M_(w)) is preferably at least 20,000and more preferably at least 30,000 up to or about 100,000 Daltons. Suchrelatively high molecular weight is achieved by driving thepolycondensation reaction to as complete a level as commerciallyfeasible using catalyst concentrations, reaction temperature and time atthe high end of the ranges disclosed in these patents. Water ofcondensation is removed as it is formed as taught in U.S. Pat. No.5,484,945 (Nagatomo et al) the disclosure in which is incorporatedherein by reference. In a preferred procedure, polycondensation isconducted at reduced pressure and 180° C. in the presence of 85%phosphoric acid as described in U.S. Pat. No. 5,142,062 (Knebel et al)the disclosure of which is also incorporated herein by reference.Succinimide (“S”) groups of formula (2) are the repeating structuralunit.

[0028] To permit formation of fibers or films from the composition (aswill be later described), S groups of the PSI are next ring-openingreacted with one or more monoamine compounds having the formula HNR₁R₂in an amount functionally effective to internally plasticize the PSI andform a poly(imide-co-amide) intermediate. R₁ represents a hydrogen atomor an alkyl or alkenyl group of 1 to 55 carbon atoms, preferably 1-30,which can be straight chain or branched and unsubstituted orsubstituted, and R₂ represents a hydrogen atom, —OH, an alkyl or alkenylgroup of 1 to 55 carbon atoms, preferably 1-30, which can be straightchain or branched and unsubstituted or substituted. The alkyl or alkenylgroups of R₁ and R₂ optionally contain one or more oxygen atoms.Optional substituents of the alkyl or alkenyl groups of R₁ and R₂ arecommon organic functional groups not interfering with the hydrolysis,acidification or crosslinking reactions of the invention such as one ofthe following: hydroxyl (—OH), ether (—OR₃), chloride (—Cl) and ketone(—COR₃), wherein R₃ represents an alkyl or alkenyl group of 1 to 8carbon atoms. Currently preferred substituents of the invention are —OHand —OR₃.

[0029] The amount of monoamine compound in the poly(imide-co-amide) isthat amount necessary to achieve adequate internal plasticization of thePSI and varies with the specific monoamine chosen. The amount ofmonoamine necessary is readily determined by one of ordinary skill andis based on the properties of the specific monoamine, e.g. molecularweight. Using diethanolamine as the monoamine, the repeating structuralunit is represented by formula (1) in combination with S groups offormula (2), the mole fraction of repeating structural units representedby formula (1) being about 0.01 to about 0.20. The internal plasticizersoftens and provides the polymer with fiber- and film-formingproperties. Any compound containing one functional amino group which isreactable with PSI can be used to form the poly(imide-co-amide)intermediate and provide the internal plasticizing function. Compoundswith two or more reactable amino groups tend to lead to crosslinking andtherefore should be avoided. Other monoamino compounds interchangeablyusable with the diethanolamine of the Example following illustrativelyinclude, but are not limited to, methylamine, ethylamine, propylamine,butylamine, pentylamine, hexylamine,O—(2-Aminopropyl)—O′—(2-methoxyethyl)polypropylene glycol 500(Jeffamine® M-600), ethanolamine, neopentanolamine,3-isononyloxypropylamine, 3-propanolamine, 2-methoxy-ethylamine,3-methoxy-propylamine, 3-ethoxypropyl-amine, ethylhexoxy-propylamine,isopropanolamine, and diisopropanol-amine. Monoamine is reacted with PSIin a solvent mixture at a temperature adequate for succinimidering-opening which is typically about 40 to 70° C. Suitable solvents forthe succinimide ring-opening reaction are water, polar organic solventssuch as dimethylformamide (DMF), dimethylsulfoxide, andN-methyl-2-pyrrolidone (NMP), and non-polar organic solvents such astoluene and hexane. The preferred solvents for the succinimidering-opening reaction are water and polar organic solvents, with waterbeing the most preferred solvent. Using diethanolamine the reaction isillustrated as follows:

[0030] wherein a and b represent the mole fractions of the respectiverepeating structural units, and a is 0.01 to 0.20 and b is 0.99 to 0.80.

[0031] Internally plasticized PSI or poly(imide-co-amide) is nexthydrolyzed with a regulated amount of base sufficient to form salt fromessentially all of the S groups of the poly(imide-co-amide) to form aninternally plasticized polyamide. As used herein, the term “essentiallyall” means>about 99%. The repeating unit of hydrolyzed succinimide, i.e.aspartate, has the following structure:

[0032] where N is an alkali metal cation such as Na⁺, K⁺, Li⁺, ammoniumor quaternary ammonium. This hydrolysis is accomplished by reacting thepoly(imide-co-amide) reaction product of the prior process step with asuitable base, e.g. alkali metal hydroxide, ammonium hydroxide, and thelike, in a suitable solvent selected from water, polar organic solventssuch as DMF, DMSO and NMP, non-polar organic solvents such as tolueneand hexane, and mixtures thereof. The currently preferred solvent iswater and the currently preferred base is sodium hydroxide. In apreferred embodiment, this hydrolysis is conveniently accomplished byadding aqueous base solution in situ to the poly(imide-co-amide)reaction product of the prior process step. In the preferred embodiment,the hydrolyzed, internally plasticized PSI composition is totallydissolved in water solution after completion of the hydrolysis.Hydrolysis occurs at room temperature or, to reduce reaction time atelevated hydrolysis temperature typically up to about 75° C., untilessentially all of the S groups are hydrolyzed.

[0033] The hydrolyzed, internally plasticized PSI composition, i.e. theinternally plasticized polyamide, is next partially acidified with aregulated amount of an acid sufficient to convert about 1 to 50% of theaspartate groups into the acid form, i.e. acidified aspartate groups,for use in the crosslinking reaction. The amount of acid to partiallyacidify the hydrolyzed, internally plasticized polyamide is that amountnecessary to reduce the pH to less than about 6.5, preferably from about4 to about 6. The repeating unit of acidified aspartate has thefollowing structure:

[0034] This partial acidification is accomplished by reacting theinternally plasticized polyamide reaction product of the prior processstep with a suitable acid in a suitable solvent selected from water,polar organic solvents such as DMF, DMSO and NMP, non-polar organicsolvents such as toluene and hexane, and mixtures thereof. Suitableacids are acids that are capable of achieving a pH of less than 5 in thepartial acidification reaction mixture and include mineral acids, e.g.hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid and thelike, and organic acids, e.g. carboxylic acids. The currently preferredsolvent is water and the currently preferred acid is hydrochloric acid.

[0035] Crosslinker for eventually crosslinking acidified ornon-acidified aspartate groups is then admixed under non-crosslinkingconditions into the solution of partially acidified, hydrolyzed,internally plasticized PSI to form a crosslinkable, uncrosslinked,partially acidified, hydrolyzed, internally plasticized, PSIcomposition. The crosslinker can be admixed with the solution ofpartially acidified, hydrolyzed, internally plasticized PSI before orafter concentration of the solution. In the preferred embodiment,crosslinker is admixed under non-crosslinking conditions into an aqueoussolution of partially acidified, hydrolyzed, internally plasticized PSIto form a crosslinkable, uncrosslinked, partially acidified, hydrolyzed,internally plasticized PSI composition. According to the invention,crosslinking is delayed until after fiber or film formation, butcrosslinker is added before fiber or film formation to insure that thecrosslinker is evenly distributed throughout the partially acidified,hydrolyzed, internally plasticized PSI solution. Adding crosslinker tothe solution while minimizing or avoiding crosslinking is accomplishedby doing so at or about room temperature (22-25° C.) down to or about 0°C. This relatively low temperature protects against prematurecrosslinking before fiber or film formation and can vary with thecrosslinking activity, or reactivity, of the crosslinker. Suchnon-crosslinking temperature conditions are chosen to avoid significantdevelopment of gel which occurs when crosslinked polyaspartate saltabsorbs solvent, e.g. water, from the solution. Such gel should beavoided since fibers cannot effectively be drawn nor films effectivelyformed from a gel-containing partially acidified, hydrolyzed, internallyplasticized PSI composition.

[0036] Suitable crosslinkers for the partially acidified, hydrolyzed,internally plasticized PSI composition according to the invention areany suitable polyfunctional compound having two or more functionalgroups that will react with the carboxylate groups of at least two ofthe aspartate groups at the pH conditions of the crosslinking reaction.Suitable crosslinkers include, but are not limited to, polyepoxides,haloepoxides (particularly chloroepoxides such as epichlorohydrin),polyaziridines, polyoxazolines, and mixtures thereof. As used herein,polyepoxides include compounds having two or more epoxide groups, e.g.diepoxides, triepoxides, and tetraepoxides. As used herein, haloepoxidesinclude compounds having two or more functional groups wherein at leastone functional group is an epoxide group and at least one functionalgroup is a halogen. As used herein, polyaziridines include compoundshaving two or more aziridine groups and polyoxazolines include compoundshaving two or more oxazoline groups. Suitable polyepoxide crosslinkersof the invention include, but are not limited to, those represented bythe formula:

[0037] wherein “e” is 2 to 6, and R₁₀ is selected from a linear orbranched aliphatic radical having 2 to 30 carbon atoms, an alicyclicradical having 3 to 18 carbon atoms, or an aromatic radical having 6 to26 carbon, wherein the radicals optionally contain one or more oxygenatoms. The R₁₀ radical will have a valency equal to “e”. As used herein,the term “aromatic” includes, but is not limited to, groups such asphenyl, naphthyl, pyridyl and the like in which the ring may besubstituted by groups which do not interfere with the crosslinkingreaction such as, but not limited to, C₁ to C₆ alkyl, nitro, halo, C₁ toC₁₂ alkoxy and the like. As used herein, the aliphatic and alicyclicgroups are optionally substituted by groups which do not interfere withthe crosslinking reaction such as, but not limited to, nitro, halo,hydroxy, C₁ to C₁₂ alkoxy and the like. When “e” is 2, the linear orbranched aliphatic radicals preferably have 2 to 14 carbon atoms and thealicyclic radicals preferably have 3 to 12 carbon atoms. When “e” is 3,the linear or branched aliphatic radicals preferably have 3 to 18 carbonatoms and the alicyclic radicals preferably have 4 to 12 carbon atoms.When “e” is 4, the linear or branched aliphatic radicals preferably have5 to 30 carbon atoms and the alicyclic radicals preferably have 5 to 18carbon atoms. When “e” is 5, the linear or branched aliphatic radicalspreferably have 6 to 30 carbon atoms and the alicyclic radicalspreferably have 6 to 18 carbon atoms. When “e” is 6, the linear orbranched aliphatic radicals preferably have 8 to 30 carbon atoms and thealicyclic radicals preferably have 8 to 18 carbon atoms.

[0038] Examples of polyepoxides for use in the invention include, butare not limited to, ethylene glycol diglycidyl ether, 1,4-cyclohexanedimethanol diglycidyl ether, diglycidyl 1,2-cyclohexane dicarboxylate,N,N-diglycidyl-4-glycidyloxyaniline, and4,4′-methylenebis(N,N-diglycidylaniline).

[0039] The polyepoxides of the invention are readily available or can beprepared by processes known in the art, such as by epoxidation ofpolyolefin with peracid.

[0040] Suitable polyaziridine crosslinkers of the invention include, butare not limited to, those represented by the formula:

[0041] wherein R₄ is an alkyl group having 1 to 10 carbon atoms which isoptionally substituted by groups which do not interfere with thecrosslinking reaction such as, but not limited to, nitro, halo, hydroxy,C₁ to C₁₂ alkoxy and the like; R₅ is an aliphatic radical having 1 to 30carbon atoms or a direct bond; X is an alkylene group having 1 to 30carbon atoms, optionally containing an ester group, an ether group, anamide group or a similar inert group; and “a” is 2 to 4. Preferredpolyaziridines are those in which R₄ is methyl, ethyl, propyl or butyl,X is represented by the formula

[0042] wherein b is 1 to 3 and c is 1 to 3, a is 2 to 3, and R₅ is apropylene radical.

[0043] Examples of polyaziridines for use in the invention include, butare not limited to, trimethylolpropane tris[(β-N-aziridinyl)propionate],and pentaerythritol tris[(β-N-aziridinyl)propionate].

[0044] The polyaziridines of the invention can be prepared by processesknown in the art such as by dehydration of α-amino hydroxyl compounds.

[0045] Suitable polyoxazoline crosslinkers of the invention include, butare not limited to, those represented by the formula:

[0046] wherein R₇ and R₈, which may be the same or different, representhydrogen, an alkyl radical having 1 to 8 carbon atoms or an aryl radicalhaving 6 to 12 carbon atoms; R₉ represents a polyfunctional, moreparticularly difunctional, alkylene radical having 1 to 20 carbon atoms,preferably 1 to 12 carbon atoms, or an arylene radical having 6 to 12carbon atoms; and d is 1 to 3.

[0047] Examples of polyoxazolines for use in the invention include, butare not limited to, ethylenebis(2-oxazoline), 1,2,4-tris(2-oxazoline)butane, and 2,2′-methylenebis[(4S)-4-phenyl-2-oxazoline].

[0048] The polyoxazolines of the invention are prepared by processesknown in the art.

[0049] The crosslinker is preferably used in anhydrous (neat),undiluted, virgin form as a solid or liquid, but alternatively can be acomponent of a dilute or concentrated solution, dispersion orsuspension. A currently preferred crosslinker is ethyleneglycoldiglycidyl ether. The amount of crosslinker according to the inventionis that amount which is sufficient to crosslink a portion of theacidified or non-acidified aspartate groups of the polyamide precursorcorresponding to about 1 to about 30%, preferably about 1 to about 15%,of the S groups in the initial homopolymer PSI. The preferred amount ofcrosslinker will depend on the specific crosslinker used. The acidifiedor non-acidified aspartate groups crosslinked during curing comprisefrom about 1 to about 30%, preferably about 1 to about 15%, of the totalsuccinimide groups originally present in the PSI. This amount and theresulting eventual level of crosslinking renders the polymer of thefibers or film superabsorbing in being capable of absorbing from atleast 3 times to more than 100 times their weight of water. Though notwishing to be bound to any particular structure, it is believed thecrosslinking agent exists as an unreacted component in the uncrosslinkedcomposition which may be intimately admixed with the balance of thecomponents of the composition, or at most is chemically reacted via onefunctional group of the crosslinker to one carboxylate group of anaspartate group but not to two which would create a crosslinkundesirably leading to gel formation.

[0050] At this stage a partially acidified, hydrolyzed, internallyplasticized, crosslinkable, uncrosslinked PSI composition exists forformation into fibers or film in a manner about to be described whichcomprises:

[0051] i) repeating, internally plasticized structural units representedby formula (3)

[0052] ii) repeating acidified aspartate structural units represented byformula (4)

[0053] iii) repeating aspartate structural units represented by formula(5)

[0054] and iv) crosslinking agent, as described herein, capable undercrosslinking reaction conditions of crosslinking units of formula (4),wherein M represents alkali metal, ammonium, quaternary ammonium ormixtures thereof, R₁ and R₂ are as defined above, and x, w and yrepresent the mole fractions of structural units (3), (4) and (5) andare respectively about 0.01 to 0.20; about 0.50 to 0.01 and about 0.40to 0.90 wherein the sum of x, w and y is 1.0.

[0055] Optionally, the partially acidifed, hydrolyzed, internallyplasticized, crosslinkable, uncrosslinked PSI contains minor amounts ofunreacted succinimide repeating units.

[0056] For the preparation of fibers, the uncrosslinked solution, whichis preferably an aqueous solution, is thickened to about 50% polymersolids concentration and a thin film of this concentrated mixture(solution) manually applied with a spatula or pipette at room (about 22°C.) temperature to the surface of a 2.5×15 cm metal plate. A secondplate of equal dimension is pressed against the film on the first plateand as the two plates with the interposed film of concentrated mixtureare manually moved apart at a slow rate at room temperature, the film isdrawn into single, long, thin, filament-like shapes which are initiallyjoined to each plate but then fracture as the plates move further apartto form elongated, shaped fibers. The unreacted crosslinker present onthe polymer fibers is substantially homogeneously distributed. Thefibers (which are essentially non-superabsorbing at this stage) aresubjected to crosslinking conditions of elevated temperature and timesufficient to cure and crosslink uncrosslinked aspartate groups of thepolymer and provide the fibers with superabsorbing capability. Analternative fiber-forming system employing a spinning die tocontinuously form and then cure fibers according to this invention isdescribed in U.S. Pat. No. 4,855,179 (Bourland et al), the fiber-formingand curing disclosure of which is incorporated herein by reference.

[0057] For the preparation of film, the uncrosslinked solution, which ispreferably an aqueous solution, can be formed into a film by anyconventional film-forming process. For example, the uncrosslinkedsolution can be thickened, e.g. to about 5% to about 50% polymer solidsconcentration, preferably about 10% to about 30%, extruded into a gasatmosphere while evaporating the solvent to form the film, the filmstretched, and then the film so formed crosslinked. The concentration ofthe polymer in the uncrosslinked solution is selected, having regard tothe molecular weight of the polymer, so as to give a solution having aviscosity that is convenient for extrusion through the extrusion diebeing used.

[0058] In another embodiment, the solution can be deposited upon asupport to form a wet film of the solution. The nature of the support isnot critical and may be selected from a variety of materials dependingon the particular application including, but not limited to, polymeric(e.g. in extruded, film and porous matrix forms), ceramic, glass, ormetallic supports. The preferred supports are the polymeric supports,particularly those in porous matrix form. Numerous techniques areavailable for the application of the solution to the support as will beapparent to those skilled in the art. For example, the polymer solutionmay be simply poured upon a level support in a quantity sufficient forit to achieve the desired uniform thickness. A blade may then be drawnover the surface of the wet film to aid the deposition of the wet filmof uniform thickness. The thickness of the wet film deposited upon thesupport is determined by the desired thickness of the film ultimatelyproduced. Generally, the wet film is deposited upon the support in asubstantially uniform thickness of about 2 to about 30 mils, preferablyabout 4 to about 10 mils. A quantity of solvent is next evaporated fromthe exposed surface of the wet film to allow the formation of arelatively thin solid layer of the exposed surface of the film. Duringthe formation of the solid layer of the exposed surface of the film, thesolvent present near the surface of the wet film is flashed off and athin coagulated skin of polymer remains. The evaporation of solvent fromthe exposed surface of the wet film may be accomplished by a variety oftechniques as will be readily apparent to those skilled in the art. Forexample, a stream of air or other gas at ambient or an elevatedtemperature below the point at which the polymer in the film willcrosslink may be simply directed at the exposed surface of the wet film.The time required to form the desired thin solid layer upon the exposedsurface of the wet film commonly ranges from about 30 minutes to about 5hours, preferably about 30 minutes to about 1 hour. The film is thencrosslinked as described herein.

[0059] Products of the curing step are partially acidified, hydrolyzed,internally plasticized, crosslinked, superabsorbing fibers or filmderived from polysuccinimide. The crosslinked fibers or film are formedof polyamide containing at least three divalent or polyvalent moietiesrandomly distributed along the polymer chain of the following formulas:

[0060] where A represents hydrogen, alkali metal cation, ammonium,quaternary ammonium or mixtures thereof, R represents a divalent orpolyvalent crosslinker moiety derived from the crosslinker used, x, yand z represent mole fractions of the moieties in the polyimide and arerespectively about 0.01 to 0.20; about 0.40 to 0.90 and about 0.01 to0.50 wherein the sum of x, y and z is 1.0, and n is an integer from 0 to4. R₁ and R₂ are substituents on the monoamine compound used for theinternal plasticization of PSI and can be the same or different.Optionally, the superabsorbent polymer contains minor amounts ofunreacted succinimide repeating units, i.e. repeating unit disclosed informula (2) above, and unreacted acidified aspartate repeating units,i.e. repeating unit disclosed in formula (4) above.

[0061] The superabsorbent fibers and film of the invention are useful inthe manufacture of moisture absorbent articles, such as disposablediapers, sanitary napkins, incontinence garments, bandages, absorbentliners in meat packing trays, pet tray liners, and the like. Thesuperabsorbent fibers and film of the invention are particularly usefulin the manufacture of thin or ultra-thin disposable diapers which haveexcellent moisture absorbance capacity, fluid distribution propertiesand reduced leakage. The superabsorbent fibers of the invention are alsouseful directly or in non-woven sheet or matting form for agriculturalor gardening materials such as water-holding materials for soils, e.g.mixing the fibers directly with soil. The superabsorbent films of theinvention are also useful directly or attached to a porous matrix foragricultural or gardening materials such as water-holding materials forsoils. The sheet or matting form can also be used for seedlings andlandscaping applications.

[0062] In making absorbent articles with the superabsorbent fibers ofthe invention, the fibers may be mixed with, attached to, layered in, ordispersed in a porous matrix of fibers. In one embodiment, thesuperabsorbent fibers of the invention are combined with other fibers toform a nonwoven material. The superabsorbent fibers of the invention canbe combined with hydrophilic fibers such as cellulose pulp or fluff,cotton liners, and synthetic fibers or a mixture of the fibers and thecellulose fluff. The fibers can be loose or joined as in nonwovens.Suitable synthetic fibers include, but are not limited to, polyesters,copolymers of polyesters and polyamides, polyvinyl alcohol and the like.The synthetic fibers may be meltblown fibers or fibers which have beentreated to render them hydrophilic. Additionally, the superabsorbentfibers of the invention may be incorporated in the absorbent article ina compartment or localized area in the absorbent structure.

[0063] In making absorbent articles with the superabsorbent films of theinvention, the films may be attached to or layered in a porous matrix offibers or a porous film. The superabsorbent films of the invention canbe combined with hydrophilic fiber matrices comprising cellulose pulp orfluff, cotton liners, and synthetic fibers or a mixture of the fibersand the cellulose fluff. Suitable synthetic fibers include, but are notlimited to, polyesters, copolymers of polyesters and polyamides,polyvinyl alcohol and the like. The synthetic fibers may be meltblownfibers or fibers which have been treated to render them hydrophilic.Additionally, the superabsorbent films of the invention may beincorporated in the absorbent article in a compartment or localized areain the absorbent structure.

[0064] Absorbent articles for use in hygienic and sanitary products,such as disposable diapers, are made with a liquid-impermeable backingmaterial, a liquid-permeable bodyside facing material and theliquid-absorbing material sandwiched between the backing material andthe facing material. The liquid-impermeable backing material can be madefrom commercially available polyolefin film and the liquid-permeablefacing material can be made from a commercially available nonwovenmaterial, such as spunbonded or corded fibrous web which is wettable andcapable of passing the fluid to be absorbed, e.g. urine.

[0065] The absorbent articles of the invention may comprise about 5% toabout 90% by weight, preferably about 20% to about 70% by weight, of thesuperabsorbent fibers or film of the invention. In an absorbent article,where the superabsorbent fibers of the invention are utilized with otherfibers in a matrix, such as a nonwoven material, or where thesuperabsorbent films are utilized in a matrix, the superabsorbent fiberor film of the invention is present in an amount from about 30 to about70 weight percent of the total matrix. In another form of absorbentarticle, the superabsorbent fiber or film may be present in acontainment structure in which the superabsorbent fiber or film of theinvention is present in an amount of about 30 to about 90 percent byweight.

EXAMPLES

[0066] The invention is further described in the following Exampleswhich is not intended to limit or restrict the invention. Unlessotherwise indicated all quantities are expressed in weight.

[0067] The tea bag test measuring superabsorbence referred to in theExample is conducted as follows: about 0.2 gm of a sample is placed in atea bag-like pouch (2″×2″) of nonwoven fabric and stapled. The tea bagis subjected to a 15 second immersion in a 0.9% saline solution, oneminute drip dry and weighing, followed by a 2 min. 45 sec. immersion,one min. drip dry and weighing, and then an additional 7 min. immersion,one min. drip dry and weighing. The absorbencies for 15 seconds, 3minutes and 10 minutes are calculated according to the followingequation and the 10 min. value reported as superabsorbing performance.Absorbency in gm/gm=(weight of the tea bag with treated sample minusweight of the wet tea bag minus weight of the untreated sample)/weightof the untreated sample.

EXAMPLE 1

[0068] Preparation of Sample Number 1: Into a round bottom flask wasadded 1 gm (10.3 mmol) polysuccinimide (MW=97,000 daltons by GPC), 0.06gm (0.98 mmol) ethanolamine and 30 gm of water. The mixture was stirredat 50° C. for 2 hours and 3.6 ml (9.00 mmol) of 10% (by w/v) NaOHsolution was added and was cooked for another 2 hours. After thereaction mixture was cooled to room temperature, 1.10 ml (1.81 mmol) of5.83% HCl (by w/w) was slowly added to reaction mixture to pH=5.5. Thereaction mixture was stirred at room temperature for another 2 hr. Theundissolved particles were removed by filtration. The filtrate wasconcentrated and the resultant thick solution (about 50% solids) wasadmixed with 0.15 gm (0.43 mmol) of a 50% aqueous ethylene glycoldiglycidyl ether. The solution was stirred at room temperatureovernight. Then a thin film of the above mixture was applied between twometal plates. Fibers were formed as the two plates were drawn apart fromeach other. Such fibers were heated in an oven at about 140° C. for 30min. to complete the crosslinking. Samples of the final product weretaken for the standard teabag test for absorbency in water and salinesolution. One gram of this SAP fiber can absorb 109 grams of water andabout 45 grams of saline solution.

[0069] Preparation of Sample Numbers 2-6: Subsequent runs were madeusing the above procedure, except that the amount of the diepoxidecrosslinking agent employed was varied as listed in Table 1. TABLE 1Crosslinker Sample Amount Absorbency¹ in Saline (0.9%) Number (mmol) 15Sec 3 min 10 min 1 0.43 41.4 43.8 45.4 2 0.17 37.2 37.2 38.7 3 0.06615.6 17.3 18.8 4 0.12 19.1 19.8 20.8 5 0.24 24.9 26.3 27.8 6 0.52 38.540.1 42.6

[0070] Preparation of Sample Numbers 7-10: Subsequent runs were madeusing the above procedure, except that the curing temperature employedwas varied as listed in Table 2. TABLE 2 Curing Sample TemperatureAbsorbency¹ in Saline (0.9%) Number (° C.) 15 Sec 3 min 10 min 7 10036.6 37.8 38.8 8 120 37.5 39.1 39.1 9 160 37.3 39.0 40.3 10 180 32.632.4 32.8

[0071] Preparation of Sample Numbers 11-15: Subsequent runs were madeusing the above procedure, except that the amount of diepoxidecrosslinking agent employed was 0.085 gms (0.24 mmol) and the curingtime employed was varied as listed in Table 3. TABLE 3 Sample Curingtime Absorbency¹ in Saline (0.9%) Number (min) 15 Sec 3 min 10 min 11 1038.0 39.1 41.4 12 20 40.2 42.5 43.5 13 40 38.0 39.1 41.4 14 60 38.5 40.142.6 15 90 34.4 36.1 36.5

[0072] Preparation of Sample Numbers 16-19: Subsequent runs were madeusing the above procedure, except that the amount of diepoxidecrosslinking agent employed was 0.12 gms (0.34 mmol) and the molecularweight (Mw) of the polysuccinimide employed was varied as listed inTable 4. TABLE 4 Sample Polysuccin- Absorbency¹ in Saline (0.9%) Numberimide, Mw 15 Sec 3 min 10 min 16 13,000 8 8.8 8.6 17 33,000 28.2 31.5 3318 51,000 36.9 39.1 41.2 19 97,000 37.2 39.2 41.8

[0073] Preparation of Sample Number 20: Into a round bottom flask wasadded 1 gm (10.3 mmol) polysuccinimide (MW=97,000 daltons by GPC), 0.125gm (1.96 mmol) ethanolamine and 30 gm of water. The mixture was stirredat 50° C. for 2 hours and 3.3 ml (8.25 mmol) of l0% (by w/v) NaOHsolution was added and was cooked for another 2 hours. After thereaction mixture was cooled to room temperature, 1.10 ml (1.81 mmol) of5.83 % HCl (by w/w) was slowly added to the reaction mixture to pH=5.5.The reaction mixture was stirred at room temperature for another 2 hr.The undissolved particles were removed by filtration. The filtrate wasconcentrated and the resultant thick solution (about 50% solids) wasadmixed with 0.18 gm (0.52 mmol) of a 50% aqueous ethylene glycoldiglycidyl ether. The solution was stirred at room temperatureovernight. Then a thin film of the above mixture was then appliedbetween two metal plates. Fibers were formed as the two plates weredrawn apart from each other. Such fibers were heated in an oven at about140° C. for 30 min. to complete the crosslinking. Samples of the finalproduct were taken for the standard teabag test for absorbency in waterand saline solution. One gram of this SAP fiber can absorb about 29grams of saline solution.

EXAMPLE 2

[0074] This example suggests that the fibers prepared according toExample 1 are biodegradable.

[0075] Superabsorbent fiber reported as sample number 20 in Example 1above were tested to determine its biodegradability.

[0076] The following experimental procedure was utilized to determinethe biodegradability of the superabsorbent fiber samples.

[0077] 1. Weighed out approximately 25 grams of Drummer soil (a siltloam soil having 18% sand, 62% silt and 20% clay with pH (1:1 soil:H₂O)of 6.7 and % organic carbon of 1.80) which had been passed through a #12sieve into each of 12 soil biodegradation flasks.

[0078] 2. Added aliquot of sample into appropriate flask.

[0079] 3. Added 25 mL of deionized water to each flask.

[0080] 4. Placed a vial containing 10 mL of 0.3 N barium hydroxide intoside chamber in each soil biodegradation test flask.

[0081] 5. Purged each test flask with air containing 70% oxygen and 30%nitrogen.

[0082] 6. Stoppered flasks with silicone stoppers.

[0083] 7. Placed flasks on rotary shaker. Rotary shaker was enclosed sothat light cannot enter.

[0084] 8. At selected time intervals removed barium hydroxide traps andreplaced with fresh barium hydroxide and again purged units with 70%oxygen:30% nitrogen air and stopper.

[0085] 9. Barium hydroxide removed from test flasks was titrated withhydrochloric acid. The total amount of carbon dioxide yielded wascalculated. The amount of carbon dioxide yielded from blank soils issubtracted from total to calculate amount of carbon dioxide yielded dueto sample.

[0086] The greater the CO₂ yielded as a % of theoretical, the greaterthe biodegradability of the sample. TABLE 5 CO₂ Yield as % ofTheoretical Days 6 13 21 28 36 41 47 CO₂ % of 8 12 16 19 23 25 28 theory

EXAMPLE 3

[0087] 5 gm (51.5 mmol)polysuccinimide (MW=65,000 daltons by GPC), 0.31gm (5.15 mmol) ethanolamine and 80 gm of water are added to a roundbottom flask. The mixture is stirred at 50° C. for 2 hours and 18.6 mlof 10% (by w/v) NaOH solution (46.35 mmol) added and held for another 2hours at 50° C. After the reaction mixture was cooled to roomtemperature, 3.60 ml (5.92 mmol) of 5.83% HCl (by w/w) was slowly addedto reaction mixture to pH=5.5. The reaction mixture was stirred at roomtemperature for another 2 hr. The undissolved particles were removed byfiltration. The filtrate was concentrated and the resultant thicksolution (about 20% solids) was admixed with 0.15 gm (1.33 mmol) of a50% aqueous ethylene glycol diglycidyl ether. The solution was stirredat room temperature overnight. The above mixture was then cast on glassplates and put into 60° C. oven overnight. The films are thenafter-treated in an oven at elevated temperature of 140° C. for 45minutes to crosslink the composition of the films. Samples of thepartially hydrolyzed, internally plasticized, crosslinked,superabsorbing films derived from polysuccinimides are subjected to thetea bag test for absorbency. One gram of film absorbs about 13 grams ofsaline solution.

[0088] Other aspects of the invention are defined as follows.

[0089] A process for preparing superabsorbing fibers or film whichcomprises: i) drawing fibers or forming film from an internallyplasticized, partially acidified, hydrolyzed, crosslinkable,uncrosslinked polysuccinimide (PSI) composition; and ii) curing thefibers or film to crosslink aspartate groups of the PSI composition ofi) to render the fibers or film superabsorbent. The aspartate groupscrosslinked during curing correspond to about 1 to about 30% of totalsuccinimide groups originally present in the PSI.

[0090] A process for rendering polymer fibers or film superabsorbentwhich comprises curing fibers or film of an internally plasticized,partially acidified, hydrolyzed, crosslinkable, uncrosslinked PSIcomposition to crosslink the composition.

[0091] In a composition capable of forming fibers or film containing afiber- or film-formable polymer, the improvement wherein the polymer isa partially acidified, hydrolyzed, internally plasticized,crosslinkable, uncrosslinked polysuccinimide.

[0092] A process for forming a partially acidified, hydrolyzed,internally plasticized polyamide which comprises (a) reactingpolysuccinimide with about 1 to about 20 mole percent of a monoaminehaving the formula HNR₁R₂ to produce a poly(imide-co-amide); wherein R₁is a hydrogen atom or an alkyl or alkenyl group of 1 to 55 carbon atomswhich can be straight chain or branched and unsubstituted orsubstituted, and R₂ is a hydrogen atom, —OH, or an alkyl or alkenylgroup of 1 to 55 carbon atoms which can be straight chain or branchedand unsubstituted or substituted; wherein the alkyl or alkenyl groups ofR₁ and R₂ optionally contain one or more oxygen atoms; and wherein theoptional substituents of the alkyl or alkenyl groups of R₁ and R₂ areselected from hydroxyl, ether, chloride or ketone; (b) reacting thepoly(imide-co-amide) of step (a) with a suitable base to hydrolyzeessentially all of the succinimide groups of the poly(imide-co-amide) ofstep (a) to produce an internally plasticized, hydrolyzed polyamide; and(c) reacting the polyamide of step (b) with a suitable acid to acidifyabout 1 to 50% of the aspartate groups of the polyamide of step (b). Asused herein, about 1 to about 20 mole percent of a monoamine is based onthe number of moles of succinimide repeating units in thepolysuccinimide, i.e. the mole ratio of monoamine to succinimiderepeating units is about 0.01 to about 0.2. In a further embodiment, thepartially acidified, hydrolyzed, internally plasticized polyamide ofstep (c) is contacted with a crosslinker under non-crosslinkingconditions to form a partially acidified, hydrolyzed, internallyplasticized, crosslinkable polyamide.

[0093] The invention is a marked departure from the level of ordinaryskill in the art by providing PSI derivatives in superabsorbing fiber orfilm form usable alone or in combination with other components(including fibers) in superabsorbing applications.

[0094] The preceding description is for illustration and should not betaken as limiting. Various modifications and alterations will be readilysuggested to persons skilled in the art. It is intended, therefore, thatthe foregoing be considered as exemplary only and that the scope of theinvention be ascertained from the following claims.

We claim:
 1. A process for preparing superabsorbing polyamide fiberscomprising: i) reacting about 1 to 20% of the succinimide groups of apolysuccinimide (PSI) with one or more monoamines to form an internallyplasticized poly(imide-co-amide) intermediate; ii) hydrolyzingessentially all of the succinimide groups of the poly(imide-co-amide)intermediate of i) to form an internally plasticized polyamide; iii)acidifying about 1 to 50% of the hydrolyzed succinimide groups of thepolyamide of ii); iv) admixing crosslinker with the partially acidifiedpolyamide of iii) under non-crosslinking conditions to form acrosslinkable, uncrosslinked, partially acidified, hydrolyzed,internally plasticized PSI composition; v) drawing fibers from thecomposition of iv); and vi) subjecting the fibers to crosslinkingconditions to crosslink a portion of uncrosslinked aspartate groups andform the superabsorbing polyamide fibers.
 2. The process of claim 1wherein the starting polysuccinimide has a weight average molecularweight of at least about 20,000 Daltons.
 3. The process of claim 2wherein the polysuccinimide of i) is prepared by condensationpolymerizing L-aspartic acid.
 4. The process of claim 1 wherein theaspartate groups crosslinked in step vi) comprise about 1 to about 50%of the total succinimide groups present in the starting PSI.
 5. Theprocess of claim 1 wherein said crosslinker is selected frompolyepoxides, haloepoxides, polyaziridines, polyoxazolines, or mixturesthereof.
 6. A process for preparing superabsorbing polyamide filmcomprising: i) reacting about 1 to 20% of the succinimide groups of apolysuccinimide (PSI) with one or more monoamines to form an internallyplasticized poly(imide-co-amide) intermediate; ii) hydrolyzingessentially all of the succinimide groups of the poly(imide-co-amide)intermediate of i) to form an internally plasticized polyamide; iii)acidifying about 1 to 50% of the hydrolyzed succinimide groups of thepolyamide of ii); iv) admixing crosslinker with the partially acidifiedpolyamide of iii) under non-crosslinking conditions to form acrosslinkable, uncrosslinked, partially acidified, hydrolyzed,internally plasticized PSI composition; v) forming film from thecomposition of iv); and vi) subjecting the film to crosslinkingconditions to crosslink a portion of uncrosslinked aspartate groups andform the superabsorbing polyamide film.
 7. The process of claim 6wherein the starting polysuccinimide has a weight average molecularweight of at least about 20,000 Daltons.
 8. The process of claim 7wherein the polysuccinimide of i) is prepared by condensationpolymerizing L-aspartic acid.
 9. The process of claim 6 wherein theaspartate groups crosslinked in step vi) comprise about 1 to about 50%of the total succinimide groups present in the starting PSI.
 10. Theprocess of claim 6 wherein said crosslinker is selected frompolyepoxides, haloepoxides, polyaziridines, polyoxazolines, or mixturesthereof.
 11. A process for preparing a partially acidified, hydrolyzed,internally plasticized polysuccinimide (PSI) composition comprising: i)reacting about 1 to 20% of the succinimide groups of a polysuccinimidepolymer having a weight average molecular weight of at least about20,000 Daltons with one or more monoamines to form an internallyplasticized poly(imide-co-amide) intermediate; ii) hydrolyzingessentially all of the succinimide groups of the poly(imide-co-amide)intermediate of i) to form an internally plasticized polyamide; and iii)acidifying about 1 to 50% of the hydrolyzed succinimide groups of thepolyamide of ii).
 12. The process of claim 11 further comprising: iv)admixing crosslinker with the partially acidified, hydrolyzed,internally plasticized polysuccinimide (PSI) composition of iii) undernon-crosslinking conditions to form a crosslinkable, uncrosslinked,partially acidified, hydrolyzed, internally plasticized PSI composition.13. The process of claim 12 wherein said crosslinker is selected frompolyepoxides, haloepoxides, polyaziridines, polyoxazolines, or mixturesthereof.
 14. The process of claim 12 further comprising: v) drawingfibers from the composition of iv).
 15. The process of claim 12 furthercomprising: v) forming film from the composition of iv).
 16. A processfor preparing superabsorbing polyamide fibers which comprises: i)drawing fibers from an internally plasticized, partially acidified,hydrolyzed, crosslinkable, uncrosslinked polysuccinimide (PSI)composition; and ii) curing the fibers to crosslink aspartate groups ofthe PSI composition of i) to render the fibers superabsorbent.
 17. Theprocess of claim 16 wherein the aspartate crosslinked in step ii)correspond to about 1 to about 50% of the total succinimide groupspresent in the PSI prior to internal plasticization and hydrolysis. 18.A process for preparing superabsorbing polyamide film which comprises:i) forming film from an internally plasticized, partially acidified,hydrolyzed, crosslinkable, uncrosslinked polysuccinimide (PSI)composition; and ii) curing the film to crosslink aspartate groups ofthe PSI composition of i) to render the film superabsorbent.
 19. Theprocess of claim 18 wherein the aspartate crosslinked in step ii)correspond to about 1 to about 50% of the total succinimide groupspresent in the PSI prior to internal plasticization and hydrolysis. 20.An internally plasticized, partially acidified, hydrolyzed,uncrosslinked PSI composition useful in forming superabsorbing polymericfibers or film comprising repeating structural units of

wherein x, y and w represent the molar fractions of repeating structuralunits of the moieties in the internally plasticized, partiallyacidified, hydrolyzed, uncrosslinked PSI composition, and arerespectively about 0.01 to 0.20, about 0.40 to 0.90 and about 0.01 to0.50 wherein the sum of x, y and w is 1.0; wherein M is an alkali metalcation, ammonium, quaternary ammonium, or mixtures thereof; wherein R₁represents a hydrogen atom or an alkyl or alkenyl group of 1 to 55carbon atoms which can be straight chain or branched and unsubstitutedor substituted, and R₂ represents a hydrogen atom, —OH, an alkyl oralkenyl group of 1 to 55 carbon atoms which can be straight chain orbranched and unsubstituted or substituted; wherein the alkyl or alkenylgroups of R₁ and R₂ optionally contain one or more oxygen atoms, and areoptionally substituted with common organic functional groups notinterfering with the hydrolysis reaction.
 21. The composition of claim20 further comprising a crosslinking agent.
 22. The process of claim 21wherein said crosslinker is selected from polyepoxides, haloepoxides,polyaziridines, polyoxazolines, or mixtures thereof.
 23. The compositionof claim 21 in fiber form.
 24. The composition of claim 21 in film form.25. Partially acidified, hydrolyzed, internally plasticized,crosslinked, superabsorbing fibers or film derived from polysuccinimide.26. The fibers or film of claim 25 comprising a polyamide having atleast three divalent or polyvalent moieties randomly distributed alongthe polymer chain having the following formulas:

wherein A represents hydrogen, an alkali metal cation, ammonium,quaternary ammonium or mixtures thereof, R represents a divalent orpolyvalent crosslinker moiety, x, y and z represent mole fractions ofthe moieties in the polyamide and are respectively about 0.01 to 0.20;about 0.40 to 0.90 and about 0.01 to 0.50 wherein the sum of x, y and zis 1.0, and n is an integer from 0 to 4; wherein R₁ represents ahydrogen atom or an alkyl or alkenyl group of 1 to 55 carbon atoms whichcan be straight chain or branched and unsubstituted or substituted, andR₂ represents a hydrogen atom, —OH, an alkyl or alkenyl group of 1 to 55carbon atoms which can be straight chain or branched and unsubstitutedor substituted; wherein the alkyl or alkenyl groups of R₁ and R₂optionally contain one or more oxygen atoms, and are optionallysubstituted with common organic functional groups selected fromhydroxyl, ether, chloride or ketone.
 27. A process for preparingsuperabsorbing polyamide fibers derived from polysuccinimide (PSI)comprising: i) drawing fibers from the internally plasticized, partiallyacidified, hydrolyzed, crosslinkable, uncrosslinked PSI composition ofclaim 20; and ii) curing the fibers to crosslink aspartate groups of thePSI composition to render the fibers superabsorbent.
 28. The process ofclaim 27 wherein the aspartate groups crosslinked during curingcorrespond to about 1 to about 50% of the total succinimide groupsoriginally present in the starting PSI.
 29. A process for preparingsuperabsorbing polyamide film derived from polysuccinimide (PSI)comprising: i) forming film from the internally plasticized, partiallyacidified, hydrolyzed, crosslinkable, uncrosslinked PSI composition ofclaim 20; and ii) curing the film to crosslink aspartate groups of thePSI composition to render the film superabsorbent.
 30. The process ofclaim 29 wherein the aspartate groups crosslinked during curingcorrespond to about 1 to about 50% of the total succinimide groupsoriginally present in the starting PSI.
 31. An absorbent articlecomprising from about 5 to about 90 percent by weight of asuperabsorbent fiber or film composition according to claim
 25. 32. Theabsorbent article of claim 31 further comprising hydrophilic fibers. 33.The absorbent article of claim 32 in fiber form wherein thesuperabsorbent fiber composition and the hydrophilic fibers are combinedto form a fiber matrix.
 34. The absorbent article of claim 31 whereinthe absorbent article is a diaper, sanitary napkin, incontinencegarment, bandage, meat packing tray absorbent liner, or pet tray liner.35. An absorbent composition comprising soil and the superabsorbentfiber or film composition according to claim 25.